1. Industrial Field of the Invention
The present invention relates to an apparatus and a method for processing lenses to be fitted in an eyeglasses frame and, more particularly, to a processing apparatus and a processing method for processing lens peripheries on the basis of information from an eyeglasses frame configuration measuring device which measures the three-dimensional configuration of lens frame portions of the eyeglasses frame. (The configuration of the lens frame portions in this specification is a locus configuration of the groove bottom of the eyeglasses frame or of the position which approximates to it, and this configuration is also referred to as an eyeglass contour.)
2. Description of the Related Art
Each of the front and rear surfaces of an eyeglasses lens has a curve for obtaining a refractive force, respectively, which corrects abnormal refraction of the user of the eyeglasses. Also, a tapered edge formed on the periphery of the lens must be designed to have a spherical curve or a curve similar to it. Generally, the eyeglasses frame in which the lenses will be fitted is processed in such a manner that the lens frame portions have a predetermined curve R to facilitate the lens fitting operation.
The ideal condition when fitting the lenses in the eyeglasses frame after the tapered edge machining is that the tapered edge curve and the curve R of the lens frame portions of the eyeglasses frame coincide with each other. In many cases, however, these curves do not coincide. In the tapered edge machining of the lenses, the selection range of the tapered edge curve is narrow. Often, the tapered edge curve does not coincide with the spherical surface R of the lens frame portions.
A conventional apparatus which has a mechanism for measuring the configuration of lens frame portions of an eyeglasses frame performs the tapered edge machining when it obtains plane information of the lens frame portions, i.e., information of projected configuration of the lens frame portions, as viewed from the front, from a device for measuring the configuration of the lens frame portions.
Recently, an apparatus for measuring a three-dimensional configuration of lens frame portions has been put into practical use. However, the three-dimensional information is only used for removing cosine errors owing to an inclination of an eyeglasses frame, and for selecting with priority a tapered edge curve which coincides with the spherical surface R of the lens frame portions.
With the above-described conventional apparatus, when the tapered edge curve coincides with the curve R of the lens frame portions, these two curves have the same peripheral length. However, in many cases, the curves do not coincide, and consequently, they are different in the peripheral length. Therefore, if the lenses having the tapered edges thus machined are fitted in the eyeglasses frame, the peripheral lengths do not coincide with each other, so that the lens fitting will not be properly carried out. Then, there is caused a problem that the eyeglasses frame must be forcibly deformed by the operator.